Ultrasonic contrast medium imaging apparatus and method

ABSTRACT

An ultrasonic enhanced-contrast imager includes an ultrasonic probe for transmitting an ultrasonic wave to an organism and receiving an ultrasonic wave from the organism, a transmitting section for transmitting an ultrasonic signal to the ultrasonic probe, a receiving section for processing a response signal ultrasonic wave received by the ultrasonic probe, a filter for extracting a specific frequency component from the processed response signal, a setting control section for setting a pass frequency band of the filter on the basis of a frequency band of the response signal from a contrast medium injected to the organism, and a control section for controlling the operation of the filter in the set pass band.

TECHNICAL FIELD

The present invention relates to an ultrasonic enhanced-contrast imagerfor obtaining imaging information required in the diagnosis of bloodflow distribution, etc. by using an ultrasonic contrast medium, and itsmethod; and, more particularly, the invention relates to a technique forattenuating a higher harmonic wave component included in a responsesignal from organic tissue, thereby making it possible to clearly imagethe distribution of the contrast medium.

BACKGROUND OF THE INVENTION

An ultrasonic enhanced-contrast imaging method and device using anultrasonic contrast medium are often used for measuring the blood flowwithin tissue. An example of such an imaging method and device aredescribed in “Ultrasound Contrast Imaging: Current and New PotentialMethods: Peter J. A. Frinking et al.” in “Ultrasound in Medicine &Biology”, Vol. 26, No. 6, p. 965, 2000.

The ultrasonic contrast medium is generally formed by mixing many airbubbles into a liquid medium, such as a physiological salt solution,etc. For example, the ultrasonic contrast medium is formed by coveringan inert gas (C₃F₈, C₄F₁₀) with a protein film or a fat film and isgenerally formed in a spherical shape. The particle diameterdistribution of the ultrasonic contrast medium is generally set to aGaussian normal distribution, and the average particle diameter isseveral μm. However, in air bubbles of 0.5 μm or less, the air bubblesgather, and become substantially larger diameter particles, so that thenormal distribution is slightly distorted.

Such a contrast medium is generally injected through a vein into theorganism. When an ultrasonic beam is irradiated to a contrast mediumthat has been injected into the organism and its sound pressure is low,the contrast medium is deformed, and acoustic information created bythis deformation is reflected and emitted from the contrast medium as aresponse signal of the ultrasonic wave. In contrast to this, when thesound pressure is high, the contrast medium is destroyed, and a strongresponse signal is emitted from the contrast medium due to thisdestruction. In each case, the ultrasonic contrast medium exhibits anonlinear response to the ultrasonic wave. When the ultrasonic wave,whose fundamental frequency component is f₀, is irradiated, the signalof a higher harmonic wave component 2f₀ is included in the responsesignal, in addition to the signal corresponding to the fundamentalfrequency component f₀.

Such behavior of the contrast medium as deformation and destruction isgenerally divided into an initial time phase and a latter time phase,depending on the time that has passed since the injection of thecontrast medium through the vein. The initial time phase is the timephase in which the ultrasonic contrast medium injected through the veinflows by blood circulation into the tissue, such as the liver, etc.,which represents the diagnostic object. The latter time phase is a timephase in which it is anticipated that the ultrasonic contrast mediumthat has flowed and been distributed into the tissue is has nowsufficiently flowed in reverse out of the tissue with the bloodcirculation after 2 to 8 minutes have passed after the injection of thecontrast medium through the vein. In the initial time phase, anultrasonic sound pressure (e.g., MI: mechanical index=0.2) forgenerating a sufficiently higher harmonic wave, without destroying thecontrast medium, is generally used. When the higher harmonic wavecomponent 2f₀ included in the response signal from the contrast mediumis detected, it is possible to grasp the distribution and flow of thecontrast medium in the tissue and blood vessels. In the latter timephase, the contrast medium will have almost all flowed out of thetissue, but one portion of the contrast medium is trapped within thetissue. A diseased portion and a healthy normal portion of the tissuediffer as to whether the contrast medium is trapped in the tissue ornot. When an ultrasonic wave having a high ultrasonic sound pressure(e.g., it is said that MI is about 0.8 or more) capable of destroyingthe contrast medium is irradiated in this latter time phase, a strongreflection signal is generated in the course of destruction of thecontrast medium. Accordingly, it is possible to discriminate the areawhere the contrast medium is trapped, i.e., the diseased portion and thearea where the contrast medium was not trapped, i.e., the healthy normalportion, by detecting the higher harmonic wave component 2f₀ included inthe response signal from the contrast medium.

The ultrasonic enhanced-contrast imager is a device for detecting thehigher harmonic wave component 2f₀ included in the response signal fromthe contrast medium and then imaging the blood flow distribution and thediseased portion within the tissue based on the position of the contrastmedium. Therefore, the 2f₀ component is conventionally extracted, andthe existence of the contrast medium is detected by using a relativelynarrow band pass filter (e.g., 1.8f₀ to 2.2f₀) having 2f₀ as a centralfrequency. Namely, since the existence of the 2f₀ component correspondsto the existence of the contrast medium, the largeness and smallness ofthe 2f₀ component indicates the spatial density distribution or thedestruction of the contrast medium. Accordingly, it is possible todetect into which part of the tissue the contrast medium has flowed, andin which part the contrast medium is trapped. In this case, since thefrequency band is narrow, there arises the problem that the depthresolution is deteriorated.

In contrast to this, methods for extracting the higher harmonic wave byutilizing a non-linearity with respect to the frequency of the contrastmedium response signal, without using a band pass filter, have beenproposed in U.S. Pat. Nos. 5,632,277 and 5,706,819. In accordance withthese methods, an ultrasonic pulse based on a first ultrasonic signal isirradiated into the organism, and its response signal is received. Then,an ultrasonic pulse based on a second ultrasonic signal obtained byinverting the polarity of the first ultrasonic signal is irradiated inthe same ultrasonic beam direction at a short time interval, and itsresponse signal is received. The component corresponding to thefundamental wave frequency f₀ within the response signal from thecontrast medium is effectively removed by adding these received signals,and the higher harmonic wave component 2f₀ is emphasized. Thus, thecontrast medium can be detected with high depth resolution without usinga band pass filter.

Further, JP-A-2000-300554 proposes a method wherein a first ultrasonicsignal has a waveform in which a period t₁ providing a signal level of apositive constant value and a period t₂ providing a signal level of anegative constant value are repeated, and a second ultrasonic signal hasa waveform obtained by inverting this first ultrasonic signal withrespect to the time axis. In accordance with this construction, thesymmetry of an ultrasonic pulse based on the first and second ultrasonicsignals is raised, and the signal of a fundamental wave component(linear component) can be lessened.

Each of these conventional techniques is effective to extract oremphasize the higher harmonic wave component 2f₀ caused by the contrastmedium. However, no consideration has been given to the case in whichthe higher harmonic wave component 2f₀, that is included in the responsesignal from the tissue, is large to such an extent that this higherharmonic wave component 2f₀ cannot be neglected in verification of thehigher harmonic wave component included in the response signal of thecontrast medium. Therefore, there are cases in which the higher harmonicwave component included in the response signal of the contrast mediumcan not be effectively extracted, such as where the tissue is relativelydeep beneath the body surface.

Namely, a nonlinear phenomenon, which here is the key to contrast mediumdetection, is also caused by propagating the ultrasonic wave within thetissue in addition to the contrast medium. In this case, the higherharmonic wave component 2f₀, having a frequency twice the fundamentalfrequency f₀ of the irradiated ultrasonic wave, is also generated. Inparticular, the strength of the signal of the higher harmonic wavecomponent 2f₀ included in the response signal from the tissue isincreased as the depth is deepened, i.e., as the propagation length ofthe ultrasonic wave is increased. Therefore, when the higher harmonicwave component 2f₀ of the tissue response signal is equivalent to orlarger than the higher harmonic wave component 2f₀ included in theresponse signal of the contrast medium, the higher harmonic wavecomponent 2f₀ of the tissue response signal prevents the detection ofthe contrast medium.

For example, the higher harmonic wave component of 2f₀ is emitted fromboth the contrast medium within the blood vessel buried into the tissue,such as in a blood vessel within the liver, and from the tissue, duringthe detection of the contrast medium. Therefore, there is a fear thatthe existence of the contrast medium will be erroneously detected.Namely, in the conventional technique for emphasizing the higherharmonic wave component of 2f₀, the 2f₀ component included in theresponse signal from the contrast medium can not always be discriminatedfrom the higher harmonic wave component 2f₀ from the organic tissue.Accordingly, there is a case in which the detecting accuracy of thehigher harmonic wave component of the contrast medium is reduced, andthe definition of an enhanced-contrast image cannot be improved.

FIGS. 2A and 2B are graphs which shows the result of a detailedexamination of the nonlinear response of the contrast medium and thetissue with respect to the ultrasonic irradiation of the fundamentalfrequency 2f₀. These graphs typically show a frequency spectrum of thereflection response signal when the ultrasonic wave of the fundamentalwave component f₀ is irradiated to the contrast medium distributed intothe tissue. The axis of abscissa shows a frequency normalized at thefundamental wave f₀, and the axis of ordinate shows the signal strengthof each frequency component. FIG. 2A shows the response signal from arelatively shallow part near a probe. FIG. 2B shows the response signalfrom a relatively deep part far from the probe. As can be seen fromthese figures, in both the shallow and deep parts, the response signal 1of the contrast medium continuously includes the higher harmonic wavecomponent over a wide frequency band, in addition to the fundamentalwave component corresponding to the fundamental frequency f₀. Incontrast to this, the response signal 2 from the tissue is divided intoa fundamental wave component 2 a of the fundamental wave frequency f₀and a higher harmonic wave component 2 b of the double higher harmonicwave 2f₀. The higher harmonic wave component 2 b is not so strong in thecase of the shallow part, but it is very strong in the case of the deeppart, and it is stronger than the response signal 1 of the contrastmedium near the double higher harmonic wave 2f₀. This is because thehigher harmonic wave component 2 b included in the response signal fromthe tissue is caused by the nonlinear effect in the propagation of theultrasonic wave within the tissue as mentioned above, so that thepropagation length is increased toward the deep part separated from theprobe. Accordingly, even when the double higher harmonic wave component2f₀ is uniformly extracted and the response signal from the contrastmedium is emphasized, as in the conventional method, the higher harmonicwave component 2f₀ of the tissue is also emphasized as well, except atshallow positions, so that the definition of a enhanced-contrast imagecannot be improved.

Therefore, an object of the present invention is to distinguish thehigher harmonic wave component included in the response signal from thecontrast medium from the higher harmonic wave component included in theresponse signal from the tissue, and to improve the definition of theenhanced-contrast image.

SUMMARY OF THE INVENTION

To achieve the above-stated object, matters relating to thecharacteristics of the ultrasonic enhanced-contrast imager of thepresent invention, as derived from the consideration of FIGS. 2A and 2B,will be presented as follows.

(1) The frequency spectrum of the response signal of the contrast mediumdoes not localize at 2f₀, but is distributed in a wide band. Thefundamental wave component of the response signal of the contrast mediumis not inferior to the fundamental wave component of the response signalof the tissue, but rather is stronger. The higher harmonic wave of theresponse signal of the tissue is very weak in comparison with the higherharmonic wave component of the contrast medium in the case of arelatively low ultrasonic sound pressure and in shallow tissue. Thesefeatures suggest that it is not necessary to limit the response signalbeing detected to the double higher harmonic wave component 2f₀ toextract the response signal from the contrast medium. Simultaneously,the contribution of the higher harmonic wave component included in theresponse signal of the tissue is not uniform in accordance with thedeepness and shallowness of the part of the contrast medium beingdetected and the largeness and smallness of the irradiated ultrasonicsound pressure. Accordingly, in accordance with the present invention,the response signal from the contrast medium is detected over a wideband by varying the band width of the band pass filter in accordancewith the size of the double higher harmonic wave component from theorganic tissue, so that the definition of a contrast medium image isimproved (first feature of the present invention).

(2) The above-mentioned wide band distribution is more notable as thefrequency spectrum of the transmitted ultrasonic signal becomes wider.The response signal of the contrast medium strongly depends on theparticle diameter of the contrast medium, and it is greatly emphasizedat a free resonance frequency f_(R) of the contrast medium. However,since the contrast medium has a particle diameter distribution, responsesignals from more of the contrast media particles within the wholeparticle diameter distribution can be expected when the ultrasonic waveover a wide band is irradiated (second feature of the presentinvention).

(3) The higher harmonic wave included in the response signal of theorganic tissue is comparatively localized near 2f₀ irrespective of thestrength of the ultrasonic sound pressure. This is because the nonlinearresponse of the tissue and of the contrast medium is greatly different.The contrast medium has notable non-linearity and shows a responsehaving a wide band with respect to the irradiated fundamental wavecomponent f₀, but the organic tissue has only secondary effects in itsnon-linearity. Therefore, in the ultrasonic signal irradiated to thecontrast medium, the spectrum of the response signal of the contrastmedium is discriminated from the double higher harmonic wave 2f₀included in the response signal from the organic tissue by performingfrequency modulation, with f₀ as a central frequency, and shifting thespectrum of the response signal of the contrast medium from frequenciesnear 2f₀, so that the improvement of the definition of the contrastmedium image can be expected. This shift effect is particularly notableif irradiation is performed twice, and addition and subtraction betweenthe response signals is carried out (third feature of the presentinvention).

(4) The non-linearity shown by the contrast medium is generallydetermined by the frequency, the amplitude and the phase of theultrasonic sound pressure waveform first irradiated to the contrastmedium, but it is almost uninfluenced by the frequency, the amplitudeand the phase of a subsequent waveform. Accordingly, if first and secondirradiations with differing frequencies, amplitudes and phases arecarried out in a double irradiation system and the effective differencesbetween the two responses of each radiation time are detected, it ispossible to extract the non-linearity proper to the contrast mediumwhich in not present in the non-linearity of the organic tissue. Thus,the spectrum of the response signal of the contrast medium isdiscriminated from the double higher harmonic wave 2f₀ included in theresponse signal from the organic tissue by further shifting the spectrumof the response signal of the contrast medium to a band lower than afrequency near 2f₀, so that the improvement of the definition of thecontrast medium image can be expected (fourth feature of the presentinvention).

(5) In contrast to the irradiation ultrasonic frequency f₀, the higherharmonic wave from the contrast medium exists, but almost no higherharmonic wave from the organic tissue exists in a frequency band of2.2f₀ or more. Accordingly, if the band of the band pass filter is setto 2.2f₀ to 2.8f₀, as in the first feature, only the response signalfrom the contrast medium is extracted. However, the contrast mediumsignal in this band has an effective signal strength only when thetransmitted wave sound pressure is sufficiently high (fifth feature ofthe present invention).

The present invention solves the above-described problems by theemploying the above-described features (1) to (5). These features of thepresent invention will now be explained in more detail.

(First Feature)

The ultrasonic enhanced-contrast method of the present invention ischaracterized in that it employs an ultrasonic probe for transmittingand receiving an ultrasonic wave travelling between the ultrasonic probeand an organism, a transmitting section for transmitting an ultrasonicsignal in the ultrasonic probe, a receiving section for processing aresponse signal of the ultrasonic wave received by said ultrasonicprobe, a filter for extracting a specific frequency component from theprocessed response signal, a frequency setting section for setting apass frequency band of said filter on the basis of the frequency band ofthe response signal from the contrast medium injected in said organism,and a control section for controlling the operation of said filter inthe set pass band.

When the fundamental frequency component of the transmitted ultrasonicsignal supplied from the ultrasonic probe is set to f₀, the pass bandwidth of the filter is set within a range of 0.8f₀ to 2.5f₀. Here, thefundamental frequency component f₀ is preferably set to a frequency neara free resonance frequency of the contrast medium, as determined by theaverage particle diameter of the contrast medium being used, and it isabout 2 MHz in the case of a contrast medium of 2 μm particle diameteras widely used.

Namely, the response signal of the contrast medium is distributed in awide frequency band, and the signal strength is also high over the widefrequency band. In consideration of these matters, the response signalover the wide frequency band 0.8f₀ to 2.5f₀ is extracted by the bandpass filter, not limiting the band pass to 2f₀ as in the conventionalmethod. Thus, the response signal of the contrast medium alone can beemphasized relative the response signal of the organic tissue localizednear 2f₀. In particular, the double higher harmonic wave component 2f₀from the organic tissue can be neglected in the case of a relativelyweak sound pressure (initial time phase) and can be also neglected withrespect to the response signal from a relatively shallow part near theprobe. Accordingly, the selection of such frequency bands is extremelyeffective. p There is a case in which the higher harmonic wave component2f₀ of the organic tissue cannot be neglected, as mentioned above, inthe case of a high sound pressure (latter period time phase) and aresponse signal from a relatively deep part far from the probe. In thiscase, the higher harmonic wave component 2f₀ of the tissue is preferablyremoved by setting the band width of the band pass filter to 0.8f₀ to1.8f₀. Namely, in this case, the higher harmonic wave component 2f₀,which is the only component emphasized in the conventional method, isremoved or attenuated. In this case, the higher harmonic wave componentcaused by the contrast medium and distributed near 2f₀ is alsoattenuated, but the response signal of the contrast medium distributedin a wide frequency band near 0.8f₀ to 1.8f₀ is extracted. Accordingly,the wide frequency band makes up for such attenuation. Therefore, thecontrast medium signal is emphasized in comparison with the tissuesignal, and contrast medium imaging of high definition can be performed.

As explained with reference to FIGS. 2A and 2B, the strength of thehigher harmonic wave component 2f₀ within the response signal from theorganic tissue is changed according to depth. Therefore, the time of theresponse signal from various depths is calculated, and the pass bandwidth of the filter is desirably switched in real time, as the depth ofthe signal changes, to 0.8f₀ to 1.8f₀, when the response signal is froma depth deeper than a set depth such that the higher harmonic wavecomponent 2f₀ is attenuated, and to 0.8f₀ to 2.5f₀, when the responsesignal is from a shallow depth. A band-pass filter (pass band 0.8f₀ to1.8f₀) and a band removing filter (removing band 1.8f₀ to 2.2f₀) having2f₀ as a central frequency can be used as the filter for attenuating thehigher harmonic wave component 2f₀.

In the band selection of the above-described filter, the fundamentalwave component f₀ from the contrast medium is also extracted. However,the fundamental wave component of the organic tissue response signalexisting near f₀ also includes a component caused by the breathing of ahuman body and heart pulsation. Accordingly, there is a case in which anartifact is caused in the contrast medium image. In this case, it issuitable to further narrow and set the pass band width of the filter to1.2f₀ to 1.8f₀. This is because the artifact superposed on thefundamental wave response f₀ component of the organic tissuedeteriorates the definition of the contrast enhanced image, since afrequency near f₀ is included as the pass band width in theabove-mentioned filter band.

Thus, in comparison with the conventional method, the SN ratio (strengthratio of the contrast medium response signal and the tissue responsesignal) of the enhanced-contrast image can be improved by discriminatingthe higher harmonic wave component 2f₀ from the tissue and the responsesignal from the contrast medium.

(Second Feature)

As mentioned above, the first feature of the present invention isdirected to the pass band width of the filter of the receiving sectionbeing greatly widened in comparison with the conventional method inaccordance with the distribution of the response signal of the contrastmedium over a wide frequency band, so as to emphasize and extract theresponse signal component of the contrast medium. To further promote theeffect of the first feature, the frequency of the ultrasonic waveirradiated to the contrast medium is preferably set over a wide band,and the ultrasonic transmitting section is desirably constructed so asto supply an ultrasonic signal, having plural frequency components, tothe ultrasonic probe. A waveform formed by connecting the unit waveformsof different frequencies can be used as such a waveform. In this case,the average of the frequency components of the unit waveforms is set tothe frequency f₀, similar to that in the feature 1.

Namely, since the contrast medium has a free resonance frequencydistributed in accordance with its particle diameter distribution, morecontrast media are efficiently made to respond to the irradiatedultrasonic wave by distributing the frequency spectrum of the irradiatedultrasonic wave in a wide band, so that the response signal of theentire contrast medium is reinforced. As a result, in contrast to theresponse signal of the organic tissue which has f₀ and 2f₀ as centers,the response signal of the contrast medium appears at a strong levelover a wider range. Accordingly, the higher harmonic wave of thecontrast medium and the higher harmonic wave of the tissue are moreeasily discriminated from each other even after passing through theband-pass filter.

(Third Feature)

In the above-described first and second features, the case ofenhanced-contrast performed on the basis of the response signal producedfrom one irradiation by the ultrasonic beam has been considered.However, the first and second features of the present invention are notlimited to an enhanced-contrast method using one irradiation, but canalso be applied to an enhanced-contrast method of a so-called doubleirradiation system (or plural irradiation system), as provided in thisfeature. The plural-time irradiation system is effective when themovement of the contrast medium and extinction due to destruction aredetected in real time and are drawn. When the movement and thedestruction of the contrast medium are detected, response signals at twodifferent times, before and after the movement, or before and after thedestruction, are required. However, in the one-time irradiation system,the time interval at a different time is generally limited by one frametime interval (e.g., 10 to 20 milliseconds). Accordingly, no one-timeirradiation system is suitable for an object having fast blood flow andin a case for instantly detecting the destruction of the contrastmedium. In a plural-time irradiation system, the ultrasonic beam isirradiated plural times in the same direction at a very short timeinterval (repetiting transmitting period: e.g., 0.1 millisecond), andthe response signal corresponding to each irradiation is compared. Thus,it is possible to detect whether the contrast medium is moved from thefocus of one ultrasonic beam to another place within a predeterminedtime interval, or whether the contrast medium is destroyed by comparingthese response signals.

More specifically, the transmitting section has a function oftransmitting M ultrasonic beams (M is a natural number of ≧2) atspecific time intervals in the same direction, and the ultrasonic signalof each time is constructed by the connection of unit waveforms ofdifferent frequencies and is transmitted so as to be asymmetrical withrespect to polarity inversion. In conformity with this construction, thereceiving section is characterized in that it constructionally has afunction of aligning phases of the response signals of the ultrasonicsignals of the plural (M) times, and a function of attenuating theresponse signal of the organic tissue by adding or subtracting thephase-processed response signals. In this case, it is preferable to setthe average frequencies f₀ of the frequency component of each unitwaveform constituting the transmitting signal of each irradiation to beequal.

Since the frequency component of each unit waveform used in thetransmitted waveform is different, frequency modulation can be said tobe performed within the waveform. When addition or subtraction isperformed on the two phase-processed response signals from such twotransmissions, it is possible to attenuate the double higher harmonicwave component 2f₀ of the response signal from the organic tissuewithout the band filter. This can be done because the non-linearresponse of the tissue and the contrast medium are greatly differentfrom each other, and the contrast medium has notable non-linearity andshows a different frequency band response, even when the transmittedfundamental wave component f₀ is slightly modulated in frequency. Theeffective difference of the frequency spectra of the two irradiationsdemonstrates a shift to the low frequency side (1.5f₀) of the spectrumof the response signal from the contrast medium. Namely, the frequencyspectrum of the response signal of the contrast medium obtained by theadding or subtracting processing is emphasized in a band near 1.2f₀ to1.8f₀ and is attenuated near 2f₀. Thus, if the 1.5f₀ component isextracted, it can be discriminated from the double higher harmonic wave2f₀, including the response signal from the organic tissue. Aspreviously mentioned, this is because the higher harmonic wave from theorganic tissue localizes near 2f₀ in spite of such frequency modulationbias. Such an effective difference using two irradiations, with only thepolarity inverted and without performing frequency modulation as in theconventional method exhibits a peak at 2f₀, without causing such ashift. Therefore, it is difficult to discriminate and efficientlyextract the higher harmonic wave component included in the responsesignal of the contrast medium from the higher harmonic wave componentincluded in the response signal of the organic tissue because ofsuperposition on the higher harmonic wave component by the organictissue response signal localized near 2f₀.

In the construction of the above-described transmitting section, it ispreferable that the transmitting section has a function of transmittingthe ultrasonic beam plural (M, a natural number of M≧2) times at aspecific time interval in the same direction, and N-waveformsrespectively having frequencies f1, f2, . . . , fn, . . . , fN (N is anatural number of N≧2) are connected. The frequency distribution widthΔf of the frequencies f1 to fN is set within a range of 0.0f₀ to 0.4f₀,where the average frequency of the frequencies f1 to fN is set to f₀,and the ultrasonic signals are transmitted so as to be asymmetrical withrespect to polarity inversion relative to each other. In accordance withthis construction, the response signal component of the contrast mediumcan be further emphasized. The frequency distribution width Δf is notparticularly limited, but preferably ranges from 0.1f₀ to 0.4f₀, and itis practical with regard to circuit construction if it falls in a rangeof 0.2f₀ to 0.3f₀.

A half cycle, one cycle or more of a sine wave can be used in the unitwaveform forming the above-described waveform of each irradiation.Conversely, the unit may be finely set to be ¼ cycle or ⅛ cycle, andfinally a chirp waveform alternately increasing and decreasing infrequency may be also used.

The waveform transmitted each time is represented by a code f(A, θ)prescribing a frequency f, an amplitude A and a starting phase θ. Afirst waveform is preferably set by connecting the N-unit waveforms withfrequencies f1(A1, θ1)<f2(A2, θ2)< . . . <fn(An, θn)< . . . <fN(AN, θN),and setting the amplitude to A1=A2= . . . =An = . . . =AN and thestarting phase to θ1=θ2= . . . =θn= . . . =θN=180°. A second waveform ispreferably set by connecting the N-unit waveforms with frequenciesf1′(A1′, θ1′)>f2′(A2′, θ2′)> . . . >fn′(An′, θn′)> . . . >fN′(AN′, θN′),and setting the amplitude to A1′=A2′= . . . =An′= . . . =AN′ and thestarting phase to θ1′=θ2′= . . . =θn′= . . . =θN′=θ°. Namely, in thefirst waveform and the second waveform, the frequency series of one isincreasing and the other is decreasing, the starting phases are set tobe the same, and the amplitude may be set to be the same or it may bealso different. In this case, the response signal of the organic tissueis attenuated by addition-processing the phase-processed responsesignal.

Further, the transmitted first and second waveforms are preferablyprescribed by a code f(A, θ), prescribing a frequency f, an amplitude Aand a starting phase θ. The first waveform is set by connecting theN-unit waveforms with frequencies set so as to satisfy the inequalityf1(A1, θ1)<f2(A2, θ2)< . . . <fn(An, θn)< . . . <fN(AN, θN), and settingthe amplitude to A1=A2= . . . =An= . . . =AN and the starting phase toθ1=θ2= . . . =θn= . . . =θN=180°. The second waveform is set byconnecting the N-unit waveforms with frequencies set to be f1′(A1′,θ1′)>f2′(A2′, θ2′)> . . . >fn′(An′, θn′)> . . . >fN′(AN′, θN′), settingthe amplitude to A1′=A2′= . . . =An′= . . . =AN′ and setting thestarting phase to be θ1′=θ2′= . . . =θn′= . . . =θN′=0°. In this case,the response signal from the organic tissue is attenuated by addition ofthe phase-processed response signal.

Here, this case is characterized in that the first transmitting waveformis set to a waveform having a starting phase of 180°, which starts bylowering (negative polarity side) and the N unit waveforms continue froma low frequency f1(< . . . <fN), and the second transmitting waveform isreversely set to a waveform having a staring phase of 0° and starts byrising (positive polarity side) and the N unit waveforms continue from ahigh frequency fN′(> . . . >f1′). Namely, when the ultrasonic wave istransmitted to the contrast medium with an initially falling waveform,an air bubble of the contrast medium is started from the expanded state,so that the frequency distribution of the response signal is shiftedlower than the average frequency f₀. In contrast to this, when theultrasonic wave is irradiated to the contrast medium in an initiallyrising waveform, the deformation of the contrast medium is started fromthe contracted state, so that the frequency distribution of the responsesignal is shifted higher than the average frequency f₀. Accordingly,there is the particular effect that the frequency distribution of theresponse signal of the contrast medium can be more efficiently shiftedto a frequency lower than the double higher harmonic wave 2f₀ by settingthe codes of the first and second waveforms as mentioned above, andadding and subtracting the receiving signals of the two irradiations,and it is discriminated from the double higher harmonic wave component2f₀, from the organic tissue localized near 2f₀ so that the responsesignal component of the contrast medium can be further emphasized.

In the above case, the frequency distribution widths Δf (=fN−N1) andΔf′(f1′−fN′) of f1 to fN and f1′ to fN′ are respectively preferablychanged over time within a range of 0.0f₀ to 0.4f₀ depending on thedepth of an ultrasonic irradiation focus. This is because, since nohigher harmonic wave component from the organic tissue is yet generatedat a shallow depth, no shift of the effective spectrum onto the lowfrequency side is required, and it is sufficient to set Δf=0, and thespectrum shift is required at a deep depth as the higher harmonic wavecomponent of the organic tissue is generated. For similar reasons, thefrequency distribution widths Δf and Δf′ of f1 to fN and f1′ to fN′ fora predetermined time after the injection of the contrast medium, e.g.,two minutes for irradiating the normal ultrasonic sound pressure, arepreferably set to 0.0f₀ since the higher harmonic wave component fromthe organic tissue is very weak then. Further, the frequencydistribution widths Δf and Δf′ of f1 to fN and f1′ to fN′ after thepassage of two minutes, at which time a high sound pressure fordestroying the contrast medium is irradiated, are preferably within therange of 0.0f₀ to 0.4f₀, since the higher harmonic wave component fromthe organic tissue is increased.

In this third feature, the receiving section has a filter for extractinga specific frequency component from the attenuated response signal ofthe organic tissue. The pass band width of this filter is preferably setto 0.8f₀ to 1.8f₀ with the average frequency f₀ as a reference. Inaccordance with this construction, the higher harmonic wave 2f₀ of theorganic tissue, which is unable to be removed by the above adding andsubtracting processing, is further removed, and the signal component ofthe contrast medium can be emphasized. Further, the pass band width ofthe filter is more preferably set to 1.2f₀ to 1.8f₀. This is becausedetection of an artifact due to breathing, pulsation, etc. appearingnear the fundamental frequency f₀, as previously mentioned, can berestrained in accordance with this construction. Further, the pass bandwidth of the filter can be changed over time in accordance with thedepth of the response signal or the irradiated ultrasonic soundpressure. For example, the band pass width of the filter can be widened(e.g., 0.8f₀ to 2.5f₀), in the case of a shallow part, in depth or theinitial time phase, and can be narrowed (e.g., 1.2f₀ to 1.f₀), in case adeep part is scanned or in the latter time phase.

(Fourth Feature)

The third feature is characterized in that the frequencies f1, f2, . . ., fn, . . . , fN of the respective unit waveforms forming the firstwaveform and the second waveform are gradually increased or decreased,and the response signal of the contrast medium included in the effectivedifference of the two signals is shifted to the low frequency side, andit is discriminated from the higher harmonic wave component from theorganic tissue. In contrast to this, the fourth feature characterized inis that the shift of the response signal of the contrast medium to alower frequency is further emphasized by setting the amplitude A of atleast the first half wave of the first waveform and the second waveformto be greater than the amplitude of the subsequent unit waveform. Thenon-linearity shown by the contrast medium is generally determined bythe frequency, the amplitude and the phase of the ultrasonic soundpressure waveform, first irradiated to the contrast medium, and it ishardly at all influenced by the frequency, the amplitude and the phaseof the subsequent waveform. Accordingly, in the double irradiationsystem, if different frequencies, amplitudes and phases are set in thefirst and second irradiations and the effective difference between theresponses is detected, it is possible to extract the non-linearityproper to the contrast medium and not the non-linearity of the organictissue: the spectrum shift to the low frequency side.

The present inventors have discovered this fourth feature in simulationand experimentally. Its physical theory background is not necessarilyclearly known, but it can be easily explained if the contrast medium isconsidered as a certain kind of resonance body. Namely, it is consideredthat among the sound pressure waveforms irradiating the contrast medium,the frequency, the phase and the amplitude of a starting unit waveformwill determine the starting response of the contrast medium. However,the subsequent behavior of the contrast medium, whose response is oncedetermined by the starting unit waveform, has a tendency to respondsimilarly to the response determined by the initial response, even whenthe frequency, the phase and the amplitude of the subsequent unitwaveform are changed. It can be just considered that this is because,normally, a system once resonated at a certain frequency does notreadily make a response to an input shifted from that resonancefrequency, and this tendency is all the greater in the case of thecontrast medium because of its non-linearity. The fourth feature of thepresent invention is characterized in that the shift of the frequencyspectrum is further emphasized and the contrast medium and the organictissue are effectively discriminated from each other by setting theamplitude A of the starting unit waveform to be greater than theamplitude of the subsequent unit waveforms, this occurring because ofthis initial waveform dependence of the contrast medium response, inother words, initial transient response dependence.

More specifically, the first waveform and the second waveform are set bya code f(A, θ), prescribing a frequency f, an amplitude A and a startingphase θ. The first waveform is formed by setting the frequencies of theN-unit waveforms to be f1(A1, θ1)<f2(A2, θ2)< . . . <fn(An, θn)< . . .<fN(AN, θN), setting the amplitude to A1>A2> . . . >An> . . . >AN andthe starting phase to θ1=θ2= . . . =θn= . . . =θN=180°. The secondwaveform is formed by setting the frequencies of the N-unit waveforms tobe f1′(A1′, θ1′)>f2′(A2′, θ2′)> . . . >fn′(An′, θn′)> . . . >fN′(AN′,θN′), and setting the amplitude to A1′>A2′> . . . >An′> . . . >AN′ andthe starting phase to θ1′=θ2′= . . . =θn′= . . . =θN′=0°.

In the above-described case, it is preferable to equally set the averageamplitudes of the waveform A to be (A1+ . . . +AN)/N and A′ to be (A1′+. . . +AN′)/N. As mentioned in the feature 3, in each of the amplitudedistribution widths ΔA(=A1−AN) and ΔA′(=AN′−A1) of A1 to AN and A1′ toAN′, ΔA is preferably within a range of 0.0 A to 0.5 A, depending on theultrasonic irradiation focus depth, independently of the frequencydistribution widths Δf and Δf′, or by coordinating with the frequencydistribution widths. It is also suitable to particularly set ΔA from 0.0A to 0.3 A. This is because, since no higher harmonic wave componentfrom the organic tissue is generated at a shallow depth, the abovespectrum shift is not required, and it is sufficient to set ΔA=0, andthe spectrum shift is required at a deep depth as the higher harmonicwave component of the organic tissue is grown. Accordingly, for example,ΔA=0.3 A. For similar reasons, it is preferable to set ΔA=0 in theinitial time phase after the injection of the contrast medium, and toset ΔA=0.3 A in the latter time phase.

In this example, A=A′. However, when A and A′ are set to be differentfrom each other, e.g., when A>A′, the present invention can be appliedparticularly to the case of a contrast medium distributed to a deepdepth (a depth of 7 to 10 centimeters when the signal is 2 MHz). Inparticular, at the deep tissue, the generated higher harmonic wavecomponent of the tissue is attenuated by the damping effect of thetissue. In contrast to this, the fundamental wave component of theresponse of the contrast medium is only slightly attenuated.Accordingly, at this depth, a larger contrast medium response can beobtained by irradiation at a frequency that is set as low as possible.When A>A′, the low frequency component of f1(<f1′) is emphasized since(f1+ . . . +fN)/N=(f1′+ . . . +fN′)/N=f₀. For example, when f1=f2′=1.8MHz, f2=f1′=2.2 MHz and f₀=2 MHz and A=2*A′, 1.8 MHz is emphasized bysuch amplitude weighting, and an increase in penetration of the contrastmedium due to an effective low frequency shift of the irradiatedultrasonic wave reaches about 3 centimeters with 6 dB. At the shallowdepth, such emphasis is naturally not required and A=A′ is acceptable.

Summarizing the above, in feature 4 the values of the frequencydistribution widths Δf and Δf′, the amplitude distribution widths ΔA andΔA′ and the amplitude weight (A/A′) are set independently or incoordination in the execution of the feature 4, as appropriate for theultrasonic irradiation focus depth, or the time that has passed sincethe injection of the contrast medium.

(Fifth Feature)

With respect to the irradiated ultrasonic frequency f₀, a higherharmonic wave response signal in a frequency band of 2.2 f0 or more fromthe contrast medium is generated, but almost no such wave from theorganism tissue is generated. Accordingly, if the band of the band-passfilter is set to 2.2f₀ to 2.8f₀ as in the first feature, only theresponse signal from the contrast medium is extracted. However, thecontrast medium signal in this band has an effective signal strengthonly when the transmitted wave sound pressure is sufficiently high. Ifonly the response from the contrast medium is considered, the highfrequency limit is not limited to 2.8f₀, but about 2.8f₀ is a highfrequency limit in view of the frequency characteristics of theultrasonic probe for transmitting and receiving a signal. This fifthfeature is efficient in the case of one-time irradiation, as in thefeatures 1 and 2, but it can be also applied to a case in which theirradiation is performed twice and an effective difference iscalculated, as will be described later.

In the above explanation, the transmitting waveform of the ultrasonicsignal that is supplied to the ultrasonic probe has been described, butthe present invention also dictates the waveform of the ultrasonic soundpressure applied to the contrast medium itself for the followingreasons. In the frequency response characteristics of recent ultrasonicprobes, the relative band is 60% or more with respect to a centralfrequency, and the (electric) transmitted waveform is very similar tothe (acoustic) transmitted waveform. The effect formed with respect tothe waveform of the ultrasonic signal supplied to the ultrasonic probealso holds true with respect to the acoustic waveform, i.e., theultrasonic sound pressure waveform applied to the contrast medium.However, since it is necessary to transmit and receive the ultrasonicwave of a wider band in the fifth feature in comparison with the firstto fourth features, the frequency response of the ultrasonic probe ispreferably set to 75% or more of the central frequency. Further, aweight, such as a Hanning weight, etc., is desirably multiplied in thetime axis direction in transmitted wave signals having a sine wave ofone cycle as the unit waveform and connected unit waveforms withdifferent amplitude and frequency. This is because, since the initialwaveform dependence and the initial transient response dependence of thecontrast medium are used in the features 3 and 4, the rapid rise andfall of the starting waveform cause an unnecessary response from thecontrast medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of an ultrasonicenhanced-contrast imager according to a first embodiment of the presentinvention.

FIGS. 2A and 2B are graphs showing a model response spectrum of acontrast medium and of tissue, illustrating features of the presentinvention.

FIG. 3 is a graph showing one example of the transmission waveform of anultrasonic wave in accordance with the first embodiment of the presentinvention.

FIGS. 4A and 4B are graphs showing one example of the ultrasonictransmission waveform of two irradiations relating to frequency emphasisof the first embodiment of the present invention, and the simulationresult of frequency spectra of a transmission signal and a responsesignal obtained by this transmission waveform.

FIGS. 5A and 5B are graphs showing one example of the ultrasonictransmission waveform of two irradiations relating to frequency andamplitude emphasis of a second embodiment of the present invention, andthe simulation result of frequency spectra of a transmission signal anda response signal obtained by this transmission waveform.

FIGS. 6A and 6B are graphs showing another example of the ultrasonictransmission waveform of the two irradiations relating to the frequencyand the amplitude emphasis of the second embodiment of the presentinvention, and the simulation result of frequency spectra of thetransmission signal and the response signal obtained by thistransmission waveform.

FIGS. 7A and 7B are graphs showing one example of the transmissionwaveform of two irradiations as used in the prior art, and thesimulation result of frequency spectra of its transmission signal and anobtained response signal to compare the prior art and the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained on the basis of the embodimentsshown in the drawings; however, the present invention is not limited tothese embodiments.

First Embodiment

FIG. 1 is a block diagram showing the overall configuration of anultrasonic enhanced-contrast imager according to a first embodiment ofthe present invention. This embodiment is suitable for the execution ofthe afore-mentioned first and second features of the present invention.As shown in FIG. 1, an ultrasonic enhanced-contrast imager 100 comprisesan ultrasonic probe 10, a transmitting section 20, a receiving section30, an image making display section 40 and a system control section 50.The transmitting section 20 comprises an arbitrary waveform generator 21and a transmitter 22. The receiving section 30 comprises a receiver 31,a phasing adder 32, a line adding/subtracting unit 33, a band-passfilter 34 and a bypass circuit 35.

When the first feature is realized, the arbitrary waveform generator 21of the transmitting section 20 is constructed so as to generate anultrasonic pulse signal having a single frequency component f₀. When thesecond feature is realized, the arbitrary waveform generator 21 isconstructed so as to generate an ultrasonic signal comprising unitwaveforms having different frequency components f1, f2, and having f₀ astheir average frequency, as in a waveform 51 shown in FIG. 3. The outputof the arbitrary waveform generator 21 is supplied to the ultrasonicprobe 10 of a wide band type through the transmitter 22. As shown inFIG. 1, the ultrasonic probe 10 is an array type probe, and isconstructed to include several hundred element vibrators. Poweramplifiers of a required number of channels corresponding to the numberof elements of the array type ultrasonic probe 10 are arranged inparallel in an output section of the transmitter 22. Thus, theultrasonic pulse of the average frequency f₀ is irradiated from theultrasonic probe 10 to tissue. A response signal from a contrast mediumdistributed in the tissue and a response signal from the tissue itselfare received by the ultrasonic probe 10 as a mixed ultrasonic signal. Asshown in FIG. 2, the response signal from the contrast medium includes ahigher harmonic wave component over a wide frequency band in addition tothe component of the fundamental wave f₀. The response signal from thetissue includes the component of the fundamental wave f₀ and thecomponent of a double higher harmonic wave 2f₀.

The response signal received by the ultrasonic probe 10 is inputted tothe receiver 31. The receiver 31 has a preamplifier of a required numberof channels corresponding to the number of elements of the ultrasonicprobe 10, a TGC amplifier, an A/D converter, etc. The receiver 31amplifies and processes the inputted response signal and then itconverts the processed signal to a digital signal, and outputs thedigital signal to the phasing adder 32. The phasing adder 32 phases andadds a delay difference or a phase difference of the response signalsfrom plural element vibrators relating to one ultrasonic beam. As iswell known, the operation of such a phasing adder accomplishes scanningand focus of the ultrasonic beam, but the phasing adder is desirably aso-called digital beam former to minimize the generation of distortionduring addition processing. This is so that no unnecessary higherharmonic wave 2f₀ component is generated by the phasing additionprocessing.

The response signal phased and added by the phasing adder 32 is suppliedto the band-pass filter 34. The band width of the band-pass filter 34can be variably adjusted by the system control section 50, as will bedescribed later. The adjustment of the band-pass width can be realizedby using, as the band-pass filter 34, a digital filter, known as an FIRfilter, and varying each coefficient series of this digital FIR filterin accordance with the depth or the ultrasonic sound pressure by thesystem control section 50. The digital filter preferably comprises athird order Chebyshev type filter. The response signal having afrequency component selected and extracted in the band-pass filter 34 isdirectly sent to the image making display section 40 in the realizationof the first and second features. The image making display section 40performs processing, including normal wave detection, image processingof a normal B-mode image, such as compression, Doppler processing, suchas a color flow, or scanning conversion processing. The same processingas that of the normal B-mode image, such as wave detection, compressionand scanning conversion is performed with respect to the contrast mediummode image.

The above-described processing operation is executed a number of timesas required to cover a predetermined section or area of the organictissue by scanning in the direction of the ultrasonic beam. Thedistribution and the size of the contrast medium is then displayed in adisplay monitor section (not shown) in the form of image information,such as brightness, by the processing of the image making displaysection 40. The system control section 50 controls this series ofoperations. The characteristic operation of the embodiment of FIG. 1,constructed in this way, will be explained. With respect to thepicked-up image of the contrast medium mode executed by injecting thecontrast medium, e.g., a B-mode fault image is picked up and displayedin the display monitor in advance. The contrast mode image obtained inthe above-described operation is overlapped with this B-mode image andis displayed, or only the contrast medium mode image is independentlydisplayed.

First, in the normal B-mode imaging, an ultrasonic signal having asingle frequency in the form of the fundamental frequency f₀ isgenerated from the arbitrary waveform generator 21 on the basis of acontrol signal from the system control section 50, and wave focusprocessing is performed in the transmitter 22. Thereafter, the processedsignal is amplified and supplied to the ultrasonic probe 10, and theultrasonic beam is transmitted to the organism. A response signal fromthe organism is detected by the ultrasonic probe 10, amplified by thereceiver 31 and converted to a digital signal. Thereafter, the phases(delay times) of the response signals from the same part received byplural vibrators are combined with each other in the phasing adder 32.With respect to every response signal phased and added, the responsesignal of a specific frequency component is selected and extracted bythe band-pass filter 34. In the case of the picked-up image of thenormal B-mode, the band of the band-pass filter 34 is adjusted to havethe fundamental frequency f₀ as its central frequency. The image makingdisplay section 40 performs wave detection processing of the output ofthe band-pass filter 34, and it also performs image processing, such ascompression or scanning conversion processing, a two-dimensional image(B-mode) of the tissue, and generates this image in the display section(display).

The scanning and the generation of the contrast medium mode image inaccordance with the present invention will be explained. The basicprocedure and operation of the scanning and the generation of thecontrast medium mode image are similar to those of the normal B-modepicked-up image.

(Case Realizing the First Feature)

When the first feature of the present invention is realized by using theembodiment of FIG. 1, an ultrasonic signal having the single fundamentalfrequency f₀ is generated from the arbitrary waveform generator 21, andan ultrasonic beam (f1<f₀<f2 in FIG. 3) is transmitted to apredetermined part of the organism, as in scanning of tissue. Aspreviously mentioned, in this ultrasonic signal, a Hanning weighting isapplied in the time axis direction, and thus unnecessary response of thecontrast medium is avoided. Further, with respect to the response signalfrom the organism, amplification and phasing processing are performed bythe receiver 31 and the phasing adder 32, as in scanning of tissue.

The element relating to the first feature of the present invention isthe band-pass filter 34 for extracting, from the phase-processedresponse signal, the component from the contrast medium. Namely, asexplained with reference to FIG. 2, in comparison with the fundamentalwave component 2 a and the higher harmonic wave component 2 b of theresponse signal from the tissue, the response signal 1 from the contrastmedium has a high signal strength over a wide frequency band. Therefore,this embodiment is characterized in that the band pass width of theband-pass filter 34 is widened in comparison with the prior art, and theresponse signal from the contrast medium is emphasized with respect tothe response signal from the tissue. In particular, it is desirable tovariably adjust the band width of the band-pass filter 34 as in thefollowing cases (A), (B) and (C).

(A) The band width of the band-pass filter 34 is set to be from 0.8f₀ to2.5f₀ in the case where the contrast medium is in a shallow location. Itis set to be from 0.8f₀ to 1.8f₀ in the case of a deep location, and itis preferably set to be from 1.2f₀ to 1.8f₀ (or 1.1f₀ to 1.8f₀).

(B) In the initial time phase after the injection of the contrastmedium, the amplitude of the transmitted ultrasonic signal is set to alow sound pressure (mechanical index: MI=0.4 to about 0.7). Similar tothe case of a shallow location, the band pass width is set to be from0.8f₀ to 1.8f₀.

(C) In the latter time phase after the injection of the contrast medium,the amplitude of the transmitted ultrasonic signal is set to be a highsound pressure (mechanical index: MI=1.0 to about 1.3), and the bandwidth of the band-pass filter 34 is changed to be from 0.8f₀ to 1.8f₀,and is preferably changed to be from 1.2f₀ to 1.8f₀ (or 1.1f₀ to 1.8f₀),in coordination with the amplitude.

This is because the higher harmonic wave component 2f₀ of the tissue canbe neglected in the case of a relatively weak sound pressure and theinitial time phase. In this case, the response signal of the contrastmedium can be emphasized over the response signal of the tissue byextracting the response signal over a wide frequency band of 0.8f₀ to2.5f₀. In the case of a deep location, the higher harmonic wavecomponent 2f₀ from the tissue is strengthened, but the response signalof the contrast medium can be emphasized more than it could in the priorart, even when the response signal is extracted over the frequency bandof 0.8f₀ to 2.5f₀. In contrast to this, when a high sound pressure isused as in the latter period time phase, the higher harmonic wavecomponent 2f₀ from the tissue cannot be neglected. Accordingly, the bandwidth is set to 0.8f₀ to 1.8f₀ and the higher harmonic wave component2f₀ of the tissue is removed or attenuated. In this case, the highfrequency component from the contrast medium near 2f₀ is alsoattenuated, but the amount is slight because the whole response signalof the contrast medium is distributed over a wide frequency band. Whenthe fundamental wave component of the response signal of the tissueexisting near f₀ includes a component caused by breathing and pulsationof the human body and this causes an artifact in the contrast mediumimage, it is preferable to slightly narrow the pass band width of thefilter to be from 1.2f₀ to 1.8f₀ (or 1.1f₀ to 1.8f₀).

Switching of such a band width is controlled by the system controlsection 50 based on the set transmitting wave focus or receiving wavefocus. For example, since the depth of the response signal correspondsto the time axis of the response signal, the system control section 50sets the band width to 0.8f₀ to 2.5f₀ in a range in which thetime-related position of the response signal inputted to the band-passfilter 34 is shallower than a set depth, and the system control section50 is switched to 1.2f₀ to 1.8f₀ when the focus is in a deep range inreal time. For example, a deep location is 4 centimeters when thefundamental frequency f₀ is 2 MHz. Here, the two band widths areswitched to correspond with two depth areas to make the explanationsimple, but the band width also may be continuously narrowed in thedepth direction.

The higher harmonic wave 2f₀ of the tissue and the higher harmonic waveincluded in the response signal of the contrast medium can bediscriminated by adjusting the band width of the band-pass filter 34 inthis way. The SN ratio (strength ratio of the contrast medium responsesignal and the tissue response signal) of an enhanced-contrast image canbe improved in comparison with the prior art by detecting and extractingthe higher harmonic wave component of the response signal from thecontrast medium in order to detect and image it. The filter forattenuating the higher harmonic wave component 2f₀ may be constructed byusing the band-pass filter 34, and it also may be constructed by using aband removing filter having a central frequency of 2f₀ by changing thecoefficient series of the digital FIR filter constituting the band-passfilter.

(Case Realizing the Second Feature)

As mentioned above, in the first feature, the pass band width of theband-pass filter 34 is widened and varied in accordance with depth ofscanning, the time phase and the sound pressure so that extraction ofthe component of response signal from the contrast medium is emphasizedover the response signal from the tissue. To further promote thiseffect, the second feature of the present invention is characterized inthat the frequency spectrum of the ultrasonic wave transmitted to thecontrast medium is made wide in comparison with the conventional case.For example, the ultrasonic signal generated by the arbitrary waveformgenerator 21 is set to have frequency component units with differentrespective waveforms, so that plural frequency components make up theentire waveform, with f₀ as an average of the respective frequencycomponents, as in the waveform 51 shown in FIG. 3. Thus, a signal havingfrequency components of a range wider than that of the first feature isset. In FIG. 3, the waveform 51 has unit waveforms in which one sinewave cycle of frequencies f1, f2 is continued. The average frequency ofthese frequencies f1, f2 is f₀ (f₀=(f1+f2)/2). In the illustratedexample, f1<f2. With respect to the average frequency f₀, a frequencysuitable for the tissue and the device, matching the response band ofthe ultrasonic probe, is selected. Further, Hanning weighting is appliedin the time axis direction, and thus an unnecessary response from thecontrast medium is avoided. The effects of the present invention are thesame even with an ultrasonic signal having a waveform obtained byinverting the polarity of the waveform 51 (rising at the start), and awaveform inverted (f1>f2) with respect to the time axis. The responsesignal of the contrast medium is strengthened over a wide frequencyspectrum by transmitting an ultrasonic signal, which is constructed bythe connection of unit waveforms having such plural frequencycomponents, to the organism. Since the contrast medium has a freeresonance frequency distribution corresponding to its particle diameterdistribution, more contrast media produce a response, and the responsesignal of the contrast medium itself is reinforced by widening thefrequency spectrum of the transmitted ultrasonic wave.

In accordance with the second feature, f₀ and 2f₀ are set to be centersof the response signal from the tissue as previously mentioned. However,since the response signal of the contrast medium is at a strong levelover a wider frequency band, the higher harmonic wave of the tissue andthe higher harmonic wave of the contrast medium are more easilydiscriminated from each other. Here, the absolute value |f1−f2| of thedifference of frequencies f1, f2, i.e., the distribution width Δf of thewaveform unit frequencies, is selected within a range of 0.0f₀ to 0.4f₀.The distribution width Δf is preferably set to 0.1f₀ to 0.4f₀, and it ismore preferably set to 0.2f₀ to 0.3f₀. The output of the arbitrarywaveform generator 21 is not limited to a unit waveform series havingthe above two frequencies f1, f2, but a waveform having N(N≧2)frequencies can be used, as will be described later.

Second Embodiment

The overall configuration of an ultrasonic enhanced-contrast imageraccording to an embodiment suitable for the realization of the third andfourth features of the present invention is also shown in FIG. 1. Inthis figure, this embodiment differs from the first embodiment in that aline adding/subtracting device 33 is newly arranged between the phasingadder 32 and the band-pass filter 34. Namely, the ultrasonic signal istransmitted twice at a specific time interval in the same direction asthe ultrasonic beam, and an image emphasizing the response signal of thecontrast medium is obtained by adding and subtracting the responsesignals of the first and second ultrasonic signals.

In the third feature of the present invention in this embodiment, thearbitrary waveform generator 21 is constructed so as to generate anultrasonic signal having a first waveform 61 (or 62), as shown in FIG.4A. The first waveform 61 has the same requirements as the waveformshown in FIG. 3. The second waveform 62 is one in which the frequenciesf1 f2 of the unit waveforms in the first waveform 61 are assigned in thereverse order. However, the second waveform 62 is asymmetric withrespect to polarity inversion, as in the prior art. As will be describedlater, the first waveform 61 and the second waveform 62 can be coded forfrequency, starting phase and amplitude, and an arbitrary waveform canbe generated by connecting the coded one-cycle waveforms.

The arbitrary waveform generator 21 alternately generates the ultrasonicsignals of the first waveform 61 and the second waveform 62 of FIG. 4A,as controlled by the system control section 50, at a predetermined timeinterval in the same ultrasonic beam direction. Each waveform isinputted to the ultrasonic probe 10 through the transmitter 22. Suchwaveforms can be easily produced by having the system control section 50supply digital data, obtained by sampling analog signals of the abovefirst waveform 61 and the second waveform 62, to a D/A converter.Further, selection of the frequency f1 or f2, the control of the numberof unit waveforms to be connected, and amplitude modulation such as theHanning weight, etc., are calculated in advance, and these values arestored in a memory device, such as a memory within the system controlsection (not shown), and are selected and executed by a program forevery transmission by a computer (not shown) in the system controlsection 50.

When the ultrasonic signals of the first waveform 61 and the secondwaveform 62 are transmitted to the organism, two response signals tothese ultrasonic signals are inputted to the receiver 31. These tworesponse signals are responses to two ultrasonic beams in the samedirection, and their times of input are separated from each other by apredetermined time interval. The response signals are amplified,A/D-converted and phase information is added in the receiver 31 and thephasing adder 32, and they are outputted to the line adding/subtractingdevice 33, each of these response signals having phase information addedto it. The line adding/subtracting device 33 carries out RF adding andsubtracting calculations, taking into account the phases of the tworesponse signals, and calculates from the two response signals oneresponse signal (RF line signal) to be displayed.

Thus, with respect to the response signal obtained by adding andsubtracting the response signals of the two ultrasonic signalirradiations, the same component (linear component) included in the tworesponse signals is attenuated, and a nonlinear component, such as ahigher harmonic wave component of the contrast medium, the tissue, etc.,is emphasized and inputted to the band-pass filter 34 in the third (orfourth) feature. The band-pass filter 34 has a construction similar tothat explained in connection with the first embodiment, the pass bandwidth varying in accordance with the depth of the response signal sourceand the time phase of the contrast medium as instructed by the systemcontrol section 50, and the response signal from a specific portion ofthe contrast medium is emphasized. The system control section 50controls a series of operations relating to the arbitrary waveformgenerator 21, the receiver 31, the phasing adder 32, the lineadding/subtracting device 33 and the band-pass filter 34.

Here, the result of a simulation effectively emphasizing the responsesignal of the contrast medium using the first waveform 61 and the secondwaveform 62 to carry out contrast medium mode imaging, as shown in theFIG. 4A, will be explained. FIG. 4B shows a frequency spectrum obtainedby simulating signals outputted from the line adding/subtracting device33 when the ultrasonic signal of the first waveform 61 of FIG. 4A isfirst transmitted and the ultrasonic signal of the second waveform 62 ofthis figure is transmitted second. The axis of abscissa of FIG. 4B showsa frequency normalized at the fundamental frequency f₀, and the axis ofordinate shows signal strength normalized at the spectrum peak of atransmitting pulse. The broken line 63 in FIG. 4B shows the frequencyspectrum of a transmitting ultrasonic wave, and the solid line 64 showsthe frequency spectrum of the response signal outputted from the lineadding/subtracting device 33.

In this simulation, in the first waveform 61 of the first transmission,the frequency is f1 (=1.8 MHz) in a first cycle, and it is f2 (=2.2 MHz)in the next cycle. The average frequency f₀ of the frequencies is set tobe 2 MHz. In the second waveform 62 of the second transmission, thefrequency is f2 (=2.2 MHz) in a first cycle, and it is f1(=1.8 MHz) inthe next cycle. The average frequency f₀ of the frequencies is set to be2 MHz. The coded “frequency f (amplitude A, starting phase θ)”previously mentioned for the first waveform 61 of the first transmissionis 1.8 MHz (1.0, 180°) and 2.2 MHz (1.0, 180°). The code of the secondwaveform 62 of the second transmission is 2.2 MHz (1.0, 0°), and 1.8 MHz(1.0, 0°). Further, each of frequency variation ranges Δf, Δf′ is 0.4MHz, and the amplitude variation range AA is 0.0. In each waveform,Hanning weighting is further superposed in the time axis direction.

Further, in this simulation, the change in particle diameter of thecontrast medium is calculated by a well-known differential equation, andthis change of the contrast medium, when the sound pressure waveform ofa mechanical index: MI=0.7 is irradiated to the contrast medium of 2microns in diameter is calculated. An observation is made at anobserving point distant from the contrast medium when vibration causedby this diametrical change is emitted as a secondary sound source. Asimple air bubble within water is adopted as the contrast medium.

Here, the feature of the frequency spectrum of the response signalobtained by this embodiment, as shown in FIG. 4B, will be explained incomparison with the frequency spectrum of a double irradiation in theprior art. FIG. 7A shows an ultrasonic transmission waveform of theconventional system, and FIG. 7B shows frequency spectra of thetransmission signal and the response signal. The axes of ordinate andabscissa of these FIGS. 7A and 7B are the same as the case of FIGS. 4Aand 4B. In FIG. 7A, a first waveform 91 is that of the firsttransmission, and a second waveform 92 is that of the secondtransmission. Each of these frequencies is set to be the fundamentalfrequency f₀=2 MHz.

When the spectra of the solid line 64 of FIG. 4B and a solid line 94 ofFIG. 7B are compared with each other, it is seen that the responsesignal near the fundamental frequency f₀ is greatly attenuated in theprior art, and the higher harmonic wave component of the tissue near 2f₀is emphasized. This is suitable for so-called tissue higher harmonicwave image picking-up (called Tissue Harmonic Imaging), but the responsesignal component of the contrast medium, which is widely distributedfrom f₀ to 2f₀, is reversely attenuated. In particular, the fundamentalfrequency f₀, which is a main response signal of the contrast medium isgreatly attenuated. Accordingly, in the case of the conventional doubleirradiating system shown in FIGS. 7A and 7B, it is impossible to satisfythe requirement that the response signal of the contrast medium isdiscriminated from the higher harmonic wave of the tissue and isemphasized and displayed. This is because the higher harmonic wavecomponent of the tissue response signal locally existing near 2f₀ isalso emphasized, and the fundamental frequency f₀ component of thecontrast medium response signal, which is distributed over a wide range,is greatly attenuated when the polarities or the time axes of theultrasonic signal of the two transmissions in the prior art are mutuallyinverted.

On the other hand, in accordance with FIG. 4B, which illustrates thepresent invention, the output of the line adding/subtracting device 33has a peak of the spectrum near 1.5f₀, and it is attenuated near 2f₀ atwhich the double higher harmonic wave component from the tissuelocalizes. Accordingly, it can be seen that the spectrum of the responsesignal from the contrast medium is shifted toward low frequencies ingeneral. In the frequency modulation of an irradiation sound pressurewaveform according to the third feature of the present invention, thespectrum of the response signal from the contrast medium is shiftedtoward the low frequencies, away from the double higher harmonic wavecomponent included in the response signal from the organic tissue, whichis an obstacle to imaging of the contrast medium, so that only thecontrast medium-generated signal can be emphasized and extracted by thecontrol of various kinds of band-pass filters, to be described later.

If the discrimination ratio of the contrast medium response signal andthe higher harmonic wave of the tissue response signal is taken to bethe energy ratio (area ratio) of the spectrum in the band ranging from1.2f₀ to 1.8f₀ and the spectrum in the band ranging from 1.8f₀ to 2.2f₀,an improvement of approximately 10 dB to 20 dB is achieved in comparisonwith the prior art (FIGS. 7A and 7B).

The pass band width of the band-pass filter 34 is the same as thatdescribed relation to the second feature. Namely, a signal obtained bythe line adding/subtracting device 32 includes the response signal fromthe contrast medium over a wide band from 0.8f₀ to 2.5f₀ in the imagingof a shallow location. Accordingly, this obtained signal can be taken tobe a signal from the contrast medium and is imaged as it is. The samepass band is also set in the normal contrast medium in which the soundpressure of the ultrasonic wave is relatively low (e.g., mechanicalindex: MI value=0.2 to 0.7). In contrast to this, when the soundpressure of the ultrasonic wave is high (e.g., mechanical index: MIvalue=1.3), it is set to be from 0.8f₀ to 1.8f₀. The effect of thechange in the band in this case is the attenuation of the frequencycomponent near 2f₀. Accordingly, this attenuation can be executedinstead by the addition of a band removing filter with 2f₀ as a centralfrequency, or by the removing filter itself. In the case of a deeplocation, it is preferable to change the band width to 1.2f₀ to 1.8f₀,so as to attenuate the higher harmonic wave caused by the tissue near2f₀, and to reduce an artifact at the fundamental wave caused by bodymovement. Thus, the response signal of the contrast medium can beemphasized more in the imaging in comparison with the second feature ofthe first embodiment.

Similar effects are also obtained when the frequencies f1, f2 of thefirst waveform 61 and the second waveform 62 of FIG. 4A areinterchanged, i.e., when the relation of the frequency f1 of the firstcode and the frequency f2 of the second code is set to f1>f (not shown).

As mentioned above, in the second embodiment, each waveform of one cyclemaking up the transmission waveform of the ultrasonic wave is coded bythe frequency f, the amplitude A and the starting phase 0, and theirwaveforms are connected. In particular, the second embodiment ischaracterized in that the frequency distribution of the transmittingsignal of the ultrasonic wave that has been twice irradiated is biasedby setting the frequencies of the first cycle of the first waveform 61and the second waveform 62 to be different, as in the waveform shown inFIG. 4A. When the transmitting signal that has been emphasized infrequency in this way is transmitted twice and its response signals areadded and processed, a shift of the frequency spectrum from adistribution (FIG. 7B: prior art) having a strong signal in a band with2f₀ as a center to a distribution (FIG. 4B: the present invention)having a strong signal from 1.2f₀ to 1.8f₀ is caused as is appropriatefor the spectrum of the response signal from the contrast medium. Thespectrum of the response signal of the contrast medium is not overlappedwith the higher harmonic wave component 2f₀ from the tissue because ofthis low frequency shift so that the response signal from the contrastmedium can be emphasized and extracted by the above band-pass filter. Itshould be particularly emphasized here that this is greatly differentfrom the prior art emphasizing 2f₀.

The fourth feature of the present invention in the second embodiment canbe realized by using the ultrasonic enhanced-contrast imager shown inFIG. 1. This embodiment differs from the above-described third featurein that the arbitrary waveform generator 21 is constructed so as togenerate an ultrasonic signal in the first waveform 71 and the secondwaveform 72 shown in FIG. 5A and the first waveform 81 and the secondwaveform 82 shown in FIG. 6A. The other parts are similar to those inthe ultrasonic enhanced-contrast imager shown in FIG. 1. Accordingly,the different points will be explained chiefly.

FIGS. 5A and 6A differ from FIG. 4A in that the amplitudes of the unitwaveform of the first cycle of the first waveform and the secondwaveform are set to be greater than the amplitude of subsequent unitwaveforms. FIGS. 5B and 6B show simulation results similar to those ofFIG. 4B. Broken lines 73, 83 show frequency spectra of the transmittedultrasonic wave, and solid lines 74, 84 show frequency spectra of theresponse signal of the contrast medium with lines added and subtracted.

The codes f (A, 0) of the first waveform 71 of FIG. 5A are, in order,1.7 MHz (1.1, 180°) and 2.3 MHz (0.8, 0°), and the codes f (A, theta) ofthe second waveform 72 are, in order, 2.3 MHz (1.1, 0°) and 1.7 MHz(0.8, 180°). Their average frequency is 2 MHz. In other words, thefrequency changing width Δf is set to 0.6 MHz, as opposed to 0.4 MHz ofFIG. 4, and the amplitude changing width AA is set to 0.3, as opposed to0.0 of FIG. 4.

With the ultrasonic waveforms of FIG. 5A, the spectrum of the responsesignal from the contrast medium obtained by adding the response signalscorresponding to the two ultrasonic transmissions is shifted toward thefundamental wave f₀, and it has a peak near 1.5f₀, as can be seen fromFIG. 5B in this case. In comparison with FIG. 4B, the attenuating effectwith respect to the higher harmonic wave component 2f₀ included in theresponse signal from the tissue is slightly inferior, but thedistribution of the response signal from the contrast medium obtained bythe addition can be emphasized over the higher harmonic wave from thetissue by extraction with the band-pass filter set to 1.2f₀ to 1.8f₀.Further, as described in the third feature, when no movements of thetissue and the contrast medium caused by breathing and pulsation arenotable, the band-pass filter is further widened (0.8f₀ to 1.8f₀) infrequency and the energy ratio of higher harmonic waves from thecontrast medium with the higher harmonic wave from tissue is high sothat the discrimination ratio can be improved.

The codes f (A, 0) of the first waveform 81 of FIG. 6A are, in order,1.8 MHz (1.0, 180°) and 2.2 MHz (0.9, 0°), and the codes f (A, 0) of thesecond waveform 82 are, in order, 2.2 MHz (1.0, 0°) and 1.8 MHz (0.9,180°). Their average frequency is 2 MHz. Namely, the frequency variationrange Δf is 0.4 MHz, the same as FIG. 4A, and the amplitude variationrange AA is set to be 0.1 in contrast to 0.0 of FIG. 4A.

As a result, with the ultrasonic waveforms of FIG. 6A, the spectrum ofthe response signal from the contrast medium obtained by adding theresponse signals corresponding to the two ultrasonic transmissions isalso shifted toward the fundamental wave f₀, and it has a peak near1.5f₀, as can be seen from FIG. 6B in this case. In this case, theattenuating effect with respect to the higher harmonic wave component2f₀ included in the response signal from the tissue is 15 dB, incomparison with about 5 dB of FIG. 4B and is therefore improved.Further, the frequency component corresponding to the triple-frequencyharmonic wave in the response of the contrast medium is shifted to2.5f₀, so that it is suitable for a case in which the fifth feature forextracting a frequency band almost having no higher harmonic wave fromthe tissue is executed. In FIG. 7B, representing the prior art, and inFIGS. 4B and 5B, the corresponding spectrum peak is near 3f₀, and itshould be emphasized that this peak lies outside the frequency responserange in the ultrasonic probe having a normal ratio band, as mentionedabove.

In the above-described embodiment, the case of the double irradiation ofthe ultrasonic wave with a time interval between the two will beconsidered. In accordance with the present invention, no simulationresult is shown with respect to a case in which the ultrasonic wave isirradiated three times or more. However, for example, the device isformed so that the codes f (A, 0) of the first waveform are, in order,1.8 MHz (1.1, 180°) and 2.2 MHz (0.9, 0°), and the codes f (A, 0) of thesecond waveform are, in order, 2.0 MHz (1.1, 0°) and 2.0 MHz (1.0,180°), and the codes f (A, 0) of a third waveform are, in order, 2.2 MHz(1.1, 180°) and 1.8 MHz (1.0, 0°). Their average frequency is set to 2MHz.

In the explanation of the third and fourth features, the ultrasonic beamis irradiated in the same direction in the two signal transmissions.However, when the contrast medium is trapped to the tissue, as in thelatter period time phase, the movement of the contrast medium is slight.Accordingly, no effects of the present invention are changed even whenthe directions of the two ultrasonic beams are slightly different.

1. An ultrasonic enhanced-contrast imager for enabling enhancement of animage when utilizing a contrast medium, characterized in that itcomprises an ultrasonic probe for transmitting an ultrasonic wave to anorganism and for receiving an ultrasonic wave from the organism, atransmitting section for transmitting an ultrasonic signal to theultrasonic probe, a receiving section for processing a response signalultrasonic wave received by said ultrasonic probe, a filter forextracting a specific frequency component from the processed responsesignal, a setting control section for setting a width of the passfrequency band of said filter so as to enable discrimination of aresponse signal from a contrast medium injected to the organism withrespect to a response signal from a tissue of the organism, and acontrol section for controlling the operation of said filter in the setpass band, wherein said setting control section sets the pass band ofsaid filter to be in a range from 0.8f₀ to 2.5f₀, where f₀ is theaverage frequency of said ultrasonic signal transmitted to saidultrasonic probe.
 2. The ultrasonic enhanced-contrast imager accordingto claim 1, wherein said setting control section sets the pass bandwidth of said filter to be in the range from 0.8f₀ to 1.8f₀.
 3. Theultrasonic enhanced-contrast imager according to claim 1, wherein saidsetting control section sets the pass band width of said filter to be inthe range from 1.2f₀ to 1.8f₀.
 4. The ultrasonic enhanced-contrastimager according to claim 1, wherein said transmitting section transmitssaid ultrasonic signal having plural frequency components to saidultrasonic probe.
 5. The ultrasonic enhanced-contrast imager accordingto claim 4, wherein said ultrasonic signal has a continuous waveformformed by connecting the waveforms of different frequencies.
 6. Anultrasonic enhanced-contrast imager according to claim 1, wherein thepass band of said filter is changed over time in accordance with a depthof the response signal.
 7. An ultrasonic enhanced-contrast imageraccording to claim 6, wherein the pass band of said filter includes asecond harmonic frequency for a shallow region and excludes a secondharmonic frequency for a deep region.
 8. An ultrasonic enhanced-contrastimager according to claim 1, wherein the pass band of the filter ischanged over time in accordance with the time that has passed since theinjection of the contrast medium.
 9. An ultrasonic enhanced-contrastimager according to claim 8, wherein the pass band of the filterincludes a second harmonic frequency for an initial time phase after theinjection and excludes the second harmonic frequency for a later timephase after the injection.
 10. The ultrasonic enhanced-contrast imagerfor enabling enhancement of an image when utilizing a contrast medium,characterized in that it comprises an ultrasonic probe for transmittingan ultrasonic wave to an organism and for receiving an ultrasonic wavefrom the organism, a transmitting section for transmitting an ultrasonicsignal to the ultrasonic probe, a receiving section for processing aresponse signal ultrasonic wave received by said ultrasonic probe, afilter for extracting a specific frequency component from the processedresponse signal, a setting control section for setting the passfrequency band of said filter on the basis of the frequency band of theresponse signal from a contrast medium injected to said organism, and acontrol section for controlling the operation of said filter in the setpass band, wherein said transmitting section has means for transmittingan ultrasonic beam plural times at specific time intervals in the samedirection, and means for constructing the continuous ultrasonic signalof each beam by the connection of waveforms of different frequencies andfor generating the ultrasonic signals of the beams so as to be mutuallyasymmetrical with respect to polarity inversion, and said receivingsection phase-processes and adds together the response signals of thoseultrasonic signals of each beam which are continuous, and extracts saidspecific frequency component from the added signal using said filter.11. The ultrasonic enhancement-contrast imager according to claim 10,wherein the pass band of said filter has an upper limit which is lessthan the high frequency limit of the frequency characteristics of theultrasonic probe.
 12. The ultrasonic enhancement-contrast imageraccording to claim 10, wherein the pass band of said filter hassubstantially a frequency band of a response signal of the contrastmedium.
 13. The ultrasonic enhancement-contrast imager according toclaim 10, wherein the pass band of the filter is changed over time inaccordance with a depth of the response signal.
 14. An ultrasonicenhanced-contrast imager according to claim 13, wherein the pass band ofsaid filter includes a second harmonic frequency for a shallow regionand excludes a second harmonic frequency for a deep region.
 15. Theultrasonic enhanced-contrast imager according to claim 10, wherein thepass band of the filter is changed over time in accordance with the timethat has passed since the injection of the contrast medium.
 16. Anultrasonic enhanced-contrast imager according to claim 15, wherein thepass band of the filter includes a second harmonic frequency for aninitial time phase after the injection and excludes the second harmonicfrequency for a later time phase after the injection.
 17. An ultrasonicenhanced-contrast imager for enabling enhancement of an image whenutilizing a contrast medium, characterized in that it comprises anultrasonic probe for transmitting an ultrasonic wave to an organismwhich is reflected from the organism back to the ultrasonic probe, atransmitting section for transmitting an ultrasonic signal to theultrasonic probe, and a receiving section for processing a responsesignal ultrasonic wave received by said ultrasonic probe, wherein saidtransmitting section has means for transmitting ultrasonic beams M (anatural number ≧2) times at specific time intervals in the samedirection, and the ultrasonic signal of each beam is constructed by theconnection of waveforms of different frequency, and the signals aretransmitted so as to be mutually asymmetrical with respect to polarityinversion, and said receiving section has means for phase-processing theresponse signals of the ultrasonic signals of said plural (M)transmissions, and means for attenuating the response signal from saidtissue by adding or subtracting the phase-processed response signals.18. The ultrasonic enhanced-contrast imager according to claim 17,wherein said receiving section has a filter for extracting a specificfrequency component from the attenuated response signal of said organictissue, and the pass band of the filter is set to be from 0.8f₀ to1.8f₀, with said average frequency f₀ serving as a reference.
 19. Theultrasonic enhanced-contrast imager according to claim 17, wherein saidreceiving section has a filter for extracting a specific frequencycomponent from the attenuated response signal of said organic tissue,and the pass band of the filter is set to be from 1.2f₀ to 1.8f₀, withsaid average frequency f₀ serving as a reference.
 20. The ultrasonicenhanced-contrast imager according to claim 17, wherein said receivingsection has a filter for extracting a specific frequency component fromthe attenuated response signal of said organic tissue, and the pass bandof the filter is changed over time in accordance with the depth of saidresponse signal within a range of 0.8f₀ to 1.8f₀, with said averagefrequency f₀ serving as a reference.
 21. An ultrasonic enhanced-contrastimager for enabling enhancement of an image when utilizing a contrastmedium, characterized in that it comprises an ultrasonic probe fortransmitting an ultrasonic wave to an organism which is reflected fromthe organism back to the ultrasonic probe, a transmitting section fortransmitting an ultrasonic signal to the ultrasonic probe, and areceiving section for processing a response signal ultrasonic wavereceived by said ultrasonic probe, wherein said transmitting section hasmeans for transmitting an ultrasonic beam M (a natural number ≧2) timesat specific time intervals in the same direction, and the ultrasonicsignal of each transmission is formed by connecting N unit waveformsrespectively having frequencies f1, f2, . . . , fn, fN (N is a naturalnumber ≧2), and a frequency distribution width Δf of said f1 to fN isset within a range of 0.0f₀ to 0.4f₀, where f₀ is the average frequencyof said signals from f1 to fN, and the ultrasonic signals of eachtransmission are transmitted so as to be mutually asymmetrical withrespect to polarity inversion, and said receiving section has means forphasing-processing the response signals of the ultrasonic signals ofsaid M transmissions, and means for attenuating the response signal oftissue of said organism by adding or subtracting the phase-processedresponse signals.
 22. The ultrasonic enhanced-contrast imager accordingto claim 21, wherein said waveform of each time is represented by a codef(A, θ) prescribing a frequency f, an amplitude A and a starting phase,and comprises a first waveform formed by connecting the N-unit waveformssetting frequencies so that f1(A1, θ1)<f2(A2, θ2)< . . . <fn(An, θn)< .. . <fN(AN, θN), setting the amplitude to be A1=A2= . . . =An = . . .=AN, and setting the starting phase to be θ1=θ2= . . . =θn= . . .=θN=180°, and also comprises a second waveform formed by connecting theN-unit waveforms setting frequencies so that f1′(A1′, θ1′)>f2′(A2′,θ2′)> . . . >fn′(An′, θn′)> . . . >fN′(AN′, θN′), setting the amplitudeto be A1′=A2′= . . . =An′= . . . =AN′ and setting the starting phase tobe θ1′=θ2′= . . . =θn′= . . . =θN′=0°.
 23. The ultrasonicenhanced-contrast imager according to claim 22, wherein frequencydistribution widths Δf and Δf′ of said f1 to fN and said f1′ to fN′ arerespectively changed over time within a range of 0.0f₀ to 0.4f₀ inaccordance with the depth of an ultrasonic irradiating focus.
 24. Theultrasonic enhanced-contrast imager according to claim 23, wherein thefrequency distribution widths Δf and Δf′ of said f1 to fN and said f1′to fN′ are set to 0.0f₀ within a predetermined time after injection ofthe contrast medium, and are changed over time within the range of 0.0f₀to 0.4f₀ after the predetermined time has passed.
 25. The ultrasonicenhanced-contrast imager according to claim 21, wherein frequencydistribution widths Δf and Δf′ of said f1 to fN and said f1′ to fN′ arerespectively changed over time within a range of 0.0f₀ to 0.4f₀ inaccordance with the depth of ultrasonic irradiating focus.
 26. Theultrasonic enhanced-contrast imager according to claim 21, wherein thefrequency distribution widths Δf and Δf′ of said f1 to fN and said f1′to fN′ are set to 0.0f₀ within a predetermined time after injection ofthe contrast medium, and are changed over time within the range of 0.0f₀to 0.4f₀ after the predetermined time has passed.
 27. An ultrasonicenhanced-contrast imager for enabling enhancement of an image whenutilizing a contrast medium, characterized in that it comprises anultrasonic probe for transmitting an ultrasonic wave to an organismwhich is reflected from the organism back to the ultrasonic probe, atransmitting section for transmitting an ultrasonic signal to theultrasonic probe, and a receiving section for processing a responsesignal of the ultrasonic wave received by said ultrasonic probe, whereinsaid transmitting section has means for transmitting an ultrasonic beamM (a natural number ≧2) times at specific time intervals in the samedirection, and the ultrasonic signal of each transmission is constructedby the connection of waveforms of different frequencies, and at leastthe amplitude of its initial unit waveform is greater than the amplitudeof the continuous unit waveform group, and the ultrasonic signals ofeach transmission are set so as to be mutually asymmetrical with respectto polarity inversion and time axis inversion, and said receivingsection has means for phase-processing the response signals of theultrasonic signals of said M transmissions, and means for attenuatingthe response signal of said organic tissue by adding or subtracting thephase-processed response signals.
 28. The ultrasonic enhanced-contrastimager according to claim 27, wherein at least one of the following:frequency distribution widths Δf and Δf′, amplitude distribution widthsΔA and ΔA′ and amplitude weight (A/A′) of the ultrasonic signal of eachtransmission, is changed over time in said transmitting section inaccordance with the depth of the ultrasonic irradiating focus, or thetime that has passed since the injection of a contrast medium.
 29. Theultrasonic enhanced-contrast imager according to claim 27, wherein saidwaveforms of different frequencies are cycle waveforms whose polaritiesare alternately inverted and whose frequencies are the same.
 30. Theultrasonic enhanced-contrast imager according to claim 27, wherein saidwaveform of each time is represented by a code f(A, θ) prescribing afrequency f, an amplitude A and a starting phase θ, and comprises afirst waveform formed by connecting N unit waveforms setting thefrequencies so that f1(A1, θ1)<f2(A2, θ2)< . . . <fn(An, θn)< . . .<fN(AN, θN), setting the amplitude to be A1=A2= . . . =An= . . . =AN,and setting the starting phase to be θ1=θ2= . . . =θn= . . . =θN=180°,and also comprises a second waveform formed by connecting N unitwaveforms setting the frequencies so that f1′(A1′, θ1′)>f2′(A2′, θ2′)> .. . >fn′(An′, θn′)> . . . >fN′(AN′, θN′), setting the amplitude to sothat A1′>A2′> . . . >An′> . . . >AN′, and setting the starting phase tobe θ1′=θ2′= . . . =θn′= . . . θN′=0°.
 31. The ultrasonicenhanced-contrast imager according to claim 27, wherein said receivingsection has a filter for extracting a specific frequency component fromthe attenuated response signal from tissue, and the pass band of thefilter is set to be from 0.8f₀ to 1.8f₀, where said average frequency f₀serves as a reference.
 32. The ultrasonic enhanced-contrast imageraccording to claim 27, wherein said receiving section has a filter forextracting a specific frequency component from the attenuated responsesignal from tissue, and the pass band of the filter is set to be from1.2f₀ to 1.8f₀, with said average frequency f₀ serving as a reference.33. The ultrasonic enhanced-contrast imager according to claim 27,wherein said receiving section has a filter for extracting a specificfrequency component from the attenuated response signal from tissue, andthe pass band of the filter is changed over time in accordance with thedepth of said response signal within a range from 0.8f₀ to 1.8f₀, withsaid average frequency f₀ serving as a reference.
 34. An ultrasonicenhanced-contrast imager for enabling enhancement of an image whenutilizing a contrast medium, characterized in that it comprises anultrasonic probe for transmitting an ultrasonic wave to an organismwhich is reflected from the organism back to the ultrasonic probe, atransmitting section for transmitting an ultrasonic signal to theultrasonic probe, and a receiving section for processing a responsesignal of the ultrasonic wave received by said ultrasonic probe, whereinsaid transmitting section has means for transmitting an ultrasonic beamM (a natural number ≧2) times at a time interval in the same direction,and the ultrasonic signal of each transmission is formed by connecting Nunit waveforms respectively having frequencies f1, f2, . . . fn, . . .fN (N is a natural number≧2), and the frequency distribution width Δf ofsaid f1 through fN is set within a range of 0.0f₀ to 0.4f₀ where f0 isthe average of said frequencies f1 through fN, and at least theamplitude of its initial unit waveform is greater than the amplitude ofthe continuous unit waveform group, and the ultrasonic signals of eachtransmission are set so as to be mutually asymmetrical with respect topolarity inversion, and said receiving section has means forphase-processing the response signals of the ultrasonic signals of saidM transmissions, and means for attenuating the response signal fromtissue of said organism by adding or subtracting the phase-processedresponse signals.
 35. An ultrasonic enhanced-contrast imager forenabling enhancement of an image when utilizing a contrast medium,characterized in that it comprises an ultrasonic probe for transmittingan ultrasonic wave to an organism which is reflected from the organismback to the ultrasonic probe, a transmitting section for transmitting anultrasonic signal to the ultrasonic probe, and a receiving section forprocessing a response signal ultrasonic wave received by said ultrasonicprobe, wherein said transmitting section has means for transmitting anultrasonic beam M (a natural number ≧2) times at specific time intervalsin the same direction, and the ultrasonic signal of each transmissioncomprises half wave groups having different frequency components, and atleast the amplitude of each signal's first half wave is greater than theamplitude of the half wave group connected to this first half wave, andthese half wave groups are set so as to be mutually asymmetrical withrespect to polarity and a time axis, and said receiving section hasmeans for phase-processing the response signals to the ultrasonicsignals of said M transmissions, and means for attenuating the responsesignal of said organic tissue by adding or subtracting thephase-processed response signals.
 36. An ultrasonic enhanced-contrastimaging method for enabling enhancement of an image when utilizing acontrast medium, characterized in that it comprises a transmittingprocess for transmitting an ultrasonic signal to an ultrasonic probe fortransmitting an ultrasonic wave to an organism which is reflected fromthe organism back to the ultrasonic probe, a receiving process forprocessing a response signal ultrasonic wave received by said ultrasonicprobe, a filter process for extracting a specific frequency componentfrom the processed response signal, a setting process for setting awidth of a pass frequency band of said filter so as to enablediscrimination of a response signal from a contrast medium injected tothe organism with respect to a response signal from a tissue of theorganism, and a control process for controlling the operation of saidfilter in the set pass band, wherein the pass band of said filter is setto be in a range from 0.8f₀ to 2.5f₀ in said setting process where, f₀is the average frequency of said ultrasonic signals given to saidultrasonic probe.
 37. The ultrasonic enhanced-contrast imaging methodaccording to claim 36, wherein the pass band of said filter is set to bein the range from 0.8f₀ to 1.8f₀ in said setting process.
 38. Theultrasonic enhanced-contrast imaging method according to claim 36,wherein the pass band of said filter is set to be in the range from1.2f₀ to 1.8f₀ in said setting process.
 39. The ultrasonicenhanced-contrast imaging method according to claim 36, wherein saidultrasonic signal having plural frequency components is sent to saidultrasonic probe in said transmitting section.
 40. The ultrasonicenhanced-contrast imaging method according to claim 39, wherein saidultrasonic signal has a waveform formed by connecting waveforms ofdifferent frequencies.
 41. The ultrasonic enhanced-contrast imagingmethod for enabling enhancement of an image when utilizing a contrastmedium, characterized in that it comprises an ultrasonic probe fortransmitting an ultrasonic wave to an organism and for receiving anultrasonic wave from the organism, a transmitting section fortransmitting an ultrasonic signal to the ultrasonic probe, a receivingsection for processing a response signal ultrasonic wave received bysaid ultrasonic probe, a filter for extracting a specific frequencycomponent from the processed response signal, a setting control sectionfor setting the pass frequency band of said filter on the basis of thefrequency band of the response signal from a contrast medium injected tosaid organism, and a control section for controlling the operation ofsaid filter in the set pass band, which has a process for transmittingan ultrasonic beam plural times at specific time intervals in the samedirection, and a process for constructing the ultrasonic signal of eachtransmission by the connection of waveforms of a different frequencies,and generating the ultrasonic signals of each transmission so as to bemutually asymmetrical with respect to polarity inversion, and saidreceiving process is set so as to add the response signals to thoseultrasonic signals of each transmission which are continuous afterphase-processing the response signals, and extract said specificfrequency component from the added signal by said filter.
 42. Anultrasonic enhanced-contrast imaging method for enabling enhancement ofan image when utilizing a contrast medium, characterized in that itcomprises a transmitting process for sending an ultrasonic signal to anultrasonic probe for transmitting an ultrasonic wave to an organismwhich is reflected from the organism back to the ultrasonic probe, and areceiving process for processing a response signal ultrasonic wavereceived by said ultrasonic probe, wherein said transmitting process hasa process for transmitting an ultrasonic beam M (a natural number ≧2)times at specific time intervals in the same direction, and theultrasonic signal of each transmission is constructed by the connectionof waveforms of different frequencies, which are transmitted so as to bemutually asymmetrical with respect to polarity inversion, and saidreceiving section has a process for phase-processing the responsesignals to the ultrasonic signals of said M transmissions, and a processfor attenuating the response signal of tissue of said organism by addingor subtracting the phased and processed response signals.
 43. Theultrasonic enhanced-contrast imaging method according to claim 42,wherein said receiving process has a filter process for extracting aspecific frequency component from the attenuated response signal oftissue, and the pass band of the filter is set to be from 0.8f₀ to1.8f₀, with said average frequency f₀ serving as a reference.
 44. Theultrasonic enhanced-contrast imaging method according to claim 42,wherein said receiving process has a filter process for extracting aspecific frequency component from the attenuated response signal oftissue, and the pass band of the filter is set to be from 1.2f₀ to1.8f₀, with said average frequency f₀ serving as a reference.
 45. Theultrasonic enhanced-contrast imaging method according to claim 42,wherein said receiving process has a filter process for extracting aspecific frequency component from the attenuated response signal oftissue, and the pass band of the filter is changed over time inaccordance with the depth of said response signal within a range of from0.8f₀ to 1.8f₀, with said average frequency f₀ serving as a reference.46. An ultrasonic enhanced-contrast imaging method for enablingenhancement of an image when utilizing a contrast medium, characterizedin that it is executed by arranging an ultrasonic probe for transmittingan ultrasonic wave to an organism which is reflected from the organismback to the ultrasonic probe, a transmitting section for transmitting anultrasonic signal to the ultrasonic probe, and a receiving section forprocessing a response signal ultrasonic wave received by said ultrasonicprobe, wherein said transmitting section has means for transmitting anultrasonic beam M (a natural number ≧2) times at specific time intervalsin the same direction, and the ultrasonic signal of each transmission isformed by connecting unit waveforms respectively having frequencies f1,f2, . . . , fn, . . . , fN (N is a natural number ≧2), and a frequencydistribution width Δf of said f1 through fN is set within a range of0.0f₀ to 0.4f₀ where f0 is the average frequency of said f1 through fN,and the ultrasonic signals of each transmission is transmitted so as tobe mutually asymmetrical with respect to polarity inversion, and saidreceiving section has means for phase-processing the response signals ofthe ultrasonic signals of said M transmissions, and means forattenuating the response signal of said organic tissue by adding orsubtracting the phase-processed response signals.
 47. The ultrasonicenhanced-contrast imaging method according to claim 46, wherein saidwaveform of each transmission is represented by a code f(A, θ)prescribing a frequency f, an amplitude A and a starting phase θ, andcomprises a first waveform formed by connecting N unit waveforms settingthe frequencies so that f1(A1, θ1)<f2(A2, θ2)< . . . <fn(An, θn)< . . .<fN(AN, θN setting the amplitude so that A1=A2= . . . =An= . . . =AN andsetting the starting phase to be θ1=θ2= . . . =θn= . . . =θN=180°, andalso comprises a second waveform formed by connecting N unit waveformssetting the frequencies so that f1′(A1′, θ1′)>f2′(A2′, θ2′)> . .. >fn′(An′, θn′)> . . . >fN′(AN′, θN′), setting the amplitude so thatA1′=A2′= . . . =An′= . . . =AN′ and setting the starting phase to beθ1′=θ2′= . . . =θn′= . . . =θN′=0°.
 48. The ultrasonic enhanced-contrastimaging method according to claim 46, wherein frequency distributionwidths Δf and Δf′ of said f1 to fN and said f1′ to fN′ are respectivelychanged over time within a range of 0.0f₀ to 0.4f₀ in accordance withthe depth of an ultrasonic irradiating focus.
 49. The ultrasonicenhanced-contrast imaging method according to claim 48, wherein thefrequency distribution widths Δf and Δf′ of said f1 to fN and said f1′to fN′ are set to 0.0f₀ within a predetermined time after injection ofthe contrast medium, and are changed over time within the range from0.0f₀ to 0.4f₀ after the predetermined time has passed.
 50. Theultrasonic enhanced-contrast imaging method according to claim 46,wherein frequency distribution widths Δf and Δf′ of said f1 to fN andsaid f1′ to fN′ are respectively changed over time within a range of0.0f₀ to 0.4f₀ in accordance with the depth of the ultrasonicirradiating focus.
 51. The ultrasonic enhanced-contrast imaging methodaccording to claim 46, wherein the frequency distribution widths Δf andΔf′ of said frequencies of f1 through fN and f1′ through fN′ are set tobe 0.0f₀ within a predetermined time after injection of the contrastmedium, and are changed over time within the range of 0.0f₀ to 0.4f₀after the predetermined time has passed.
 52. An ultrasonicenhanced-contrast imaging method for enabling enhancement of an imagewhen utilizing a contrast medium, which comprises a transmitting processfor transmitting an ultrasonic signal to an ultrasonic probe fortransmitting an ultrasonic wave to an organism which is reflected fromthe organism back to the ultrasonic probe, and a receiving process forprocessing a response signal ultrasonic wave received by said ultrasonicprobe, wherein said transmitting process has a process for transmittingan ultrasonic beam M (a natural number ≧2) times at specific timeintervals in the same direction, and the ultrasonic signal of eachtransmission is constructed by the connection of a waveform of adifferent frequency, and at least the amplitude of its initial unitwaveform is greater than the amplitude of the continuous group of unitwaveforms, and the ultrasonic signals of each transmission are set so asto be mutually asymmetrical with respect to polarity inversion and timeaxis inversion, and said receiving process has a process forphase-processing the response signals of the ultrasonic signals of saidM transmissions, and a process for attenuating the response signal fromtissue of said organism by adding or subtracting the phased andprocessed response signals.
 53. The ultrasonic enhanced-contrast imagingmethod according to claim 52, wherein at least one of the followingvalues: frequency distribution widths Δf and Δf′, amplitude distributionwidths ΔA and ΔA′, and amplitude weight (A/A′) of the ultrasonic signalof each transmission in said transmitting section, is changed over timein accordance with the depth of the ultrasonic irradiating focus, or thetime which has passed since the injection of a contrast medium.
 54. Theultrasonic enhanced-contrast imaging method according to claim 52,wherein said waveforms of different frequencies are cycle waveformswhose polarities are alternately inverted and whose frequencies are thesame.
 55. The ultrasonic enhanced-contrast imaging method according toclaim 52, wherein said waveform of each transmission is represented by acode f(A, θ) prescribing a frequency f, an amplitude A and a startingphase θ, and comprises a first waveform formed by connecting N unitwaveforms setting the frequencies so that f1(A1, θ1)<f2(A2, θ2)< . . .<fn(An, θn)< . . . <fN(AN, θN), setting the amplitude to be A1=A2= . . .=An= . . . =AN and setting the starting phase to be θ1=θ2= . . . =θn= .. . =θN=180°, and also comprises a second waveform formed by continuingthe N-unit waveforms of f1′(A1′, θ1′)>f2′(A2′, θ2′)> . . . >fn′(An′,θn′)> . . . >fN′(AN′, θN′), setting the amplitude to so that A1′>A2′> .. . >An′> . . . >AN′ and the starting phase to θ1′=θ2′= . . . =θn′= . .. =θN′=0°.
 56. The ultrasonic enhanced-contrast imaging method accordingto claim 52, wherein said receiving section has a filter for extractinga specific frequency component from the attenuated response signal oftissue, and the pass band of the filter is set to be from 0.8f₀ to1.8f₀, with said average frequency f₀ serving as a reference.
 57. Theultrasonic enhanced-contrast imaging method according to claim 52,wherein said receiving section has a filter for extracting a specificfrequency component from the attenuated response signal of tissue, andthe pass band of the filter is set to be from 1.2f₀ to 1.8f₀, with saidaverage frequency f₀ serving as a reference.
 58. The ultrasonicenhanced-contrast imaging method according to claim 52, wherein saidreceiving section has a filter for extracting a specific frequencycomponent from the attenuated response signal of tissue, and the passband of the filter is changed over time in accordance with the depth ofsaid response signal within a range from 0.8f₀ to 1.8f₀, with saidaverage frequency f₀ serving as a reference.
 59. An ultrasonicenhanced-contrast imaging method for enabling enhancement of an imagewhen utilizing a contrast medium, characterized in that it comprises atransmitting process for transmitting an ultrasonic signal to anultrasonic probe for transmitting an ultrasonic wave to an organismwhich reflects an ultrasonic wave back to the ultrasonic probe, and areceiving process for processing a response signal ultrasonic wavereceived by said ultrasonic probe, wherein said transmitting process hasmeans for transmitting an ultrasonic beam M (a natural number ≧2) timesat specific time intervals in the same direction, and the ultrasonicsignal of each transmission is formed by connecting N unit waveformsrespectively having frequencies f1, f2, . . . , fn, . . . , fN (N is anatural number ≧2), and a frequency distribution width Δf of said f1through fN is set within a range from 0.0f₀ to 0.4f₀ where f₀ is theaverage frequency of said f1 through fN, and at least the amplitude ofits initial unit waveform is greater than the amplitude of thecontinuous group of unit waveforms, and the ultrasonic signal of eachtransmission are set so as to be mutually asymmetrical with respect topolarity inversion, and said receiving process has a process forphase-processing the response signals of the ultrasonic signals of saidM times, and a process for attenuating the response signal from tissueof said organism by adding or subtracting the phase-processed responsesignals.
 60. An ultrasonic enhanced-contrast imaging method for enablingenhancement of an image when utilizing a contrast medium, characterizedin that it comprises a transmitting process for transmitting anultrasonic signal to an ultrasonic probe for transmitting an ultrasonicwave to an organism which is reflected back to the ultrasonic probe, anda receiving process for processing a response signal ultrasonic wavereceived by said ultrasonic probe, wherein said transmitting process hasa process for transmitting an ultrasonic beam M (natural number ≧2)times at specific time intervals in the same direction, and theultrasonic signal of each transmission comprises a half wave grouphaving different frequency components, and at least the amplitude of itsfirst half wave is greater than the amplitude of the half wave groupconnected to this first half wave, and the half wave groups are set soas to be mutually asymmetrical with respect to polarity and time axis,and said receiving process has a process for phase-processing theresponse signals of the ultrasonic signals of said M times, and aprocess for attenuating the response signal from tissue of said organismby adding or subtracting the phase-processed response signals.
 61. Anultrasonic enhanced-contrast imager for enabling enhancement of an imagewhen utilizing a contrast medium, characterized in that it comprises anultrasonic probe for transmitting an ultrasonic wave to an organism andfor receiving an ultrasonic wave from the organism, a transmittingsection for transmitting an ultrasonic signal to the ultrasonic probe, areceiving section for processing a response signal ultrasonic wavereceived by said ultrasonic probe, a filter for extracting a specificfrequency component from the processed response signal, a settingcontrol section for setting a width of the pass frequency band of saidfilter so as to enable discrimination of a response signal from acontrast medium injected to the organism with respect to a responsesignal from a tissue of the organism, and a control section forcontrolling the operation of said filter in the set pass band, whereinthe pass band of said filter has an upper limit which is less than ahigh frequency limit of the frequency characteristics of the ultrasonicprobe.
 62. An ultrasonic enhanced-contrast imager for enablingenhancement of an image when utilizing a contrast medium, characterizedin that it comprises an ultrasonic probe for transmitting an ultrasonicwave to an organism and for receiving an ultrasonic wave from theorganism, a transmitting section for transmitting an ultrasonic signalto the ultrasonic probe, a receiving section for processing a responsesignal ultrasonic wave received by said ultrasonic probe, a filter forextracting a specific frequency component from the processed responsesignal, a setting control section for setting a width of the passfrequency band of said filter so as to enable discrimination of aresponse signal from a contrast medium injected to the organism withrespect to a response signal from a tissue of the organism, and acontrol section for controlling the operation of said filter in the setpass band, wherein the pass band of said filter has substantially afrequency band of the response signal of the contrast medium.